Instructions

• Preheat oven to 350°F (180°C).
• Trim the chicken thighs if desired: remove skin and any excess fat (including the pocket of fat on the back) using kitchen shears or a knife. Pat the thighs dry with paper towels. Season both sides of all 8–10 bone-in chicken thighs with salt and pepper.
• Heat a large frying pan over medium-high heat. Add 2–3 teaspoons olive oil (use a little more if your pan is large and needs it).
• When the oil is hot, brown the chicken thighs in batches if needed so they aren’t overcrowded. Brown well on both sides, about 10 minutes total, until the surfaces are golden. Don’t fully cook them through—just brown.
• Remove the browned thighs from the pan and place them in a glass casserole dish or similar ovenproof dish in a single layer.
• If there is a lot of fat in the pan, pour off most of it, leaving a thin coating to sauté the vegetables.
• Add the red onion slivers to the pan and cook about 2 minutes, stirring, until they begin to soften.
• Add the 8 oz sliced mushrooms to the pan and cook about 5 minutes more, stirring occasionally, until the mushroom liquid has largely evaporated.
• Stir in 1 teaspoon ground rosemary with the cooked onions and mushrooms.
• Spoon the partly-cooked onion-and-mushroom mixture evenly over the chicken pieces in the casserole dish.
• Roast in the preheated oven 35–45 minutes, until the chicken and vegetables are cooked through and the chicken juices run clear (or until an internal temperature of 165°F / 74°C is reached).
• Remove from oven, spoon any pan juices over the chicken, and garnish with fresh chopped parsley if using. Serve hot.